diff --git a/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/data/MongoItemReader.java b/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/data/MongoItemReader.java
index 43c5ea9fd..bb37a9a81 100644
--- a/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/data/MongoItemReader.java
+++ b/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/data/MongoItemReader.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -82,9 +82,9 @@ import org.springframework.util.StringUtils;
  * @author Parikshit Dutta
  */
 public class MongoItemReader<T> extends AbstractPaginatedDataItemReader<T> implements InitializingBean {
-	
+
 	private static final Logger log = LoggerFactory.getLogger(MongoItemReader.class);
-	
+
 	private MongoOperations template;
 	private Query query;
 	private String queryString;
@@ -168,6 +168,7 @@ public class MongoItemReader<T> extends AbstractPaginatedDataItemReader<T> imple
 	 * @param sorts map of properties and direction to sort each.
 	 */
 	public void setSort(Map<String, Sort.Direction> sorts) {
+		Assert.notNull(sorts, "Sorts must not be null");
 		this.sort = convertToSort(sorts);
 	}
 
@@ -252,7 +253,7 @@ public class MongoItemReader<T> extends AbstractPaginatedDataItemReader<T> imple
 	}
 
 	private Sort convertToSort(Map<String, Sort.Direction> sorts) {
-		List<Sort.Order> sortValues = new ArrayList<>();
+		List<Sort.Order> sortValues = new ArrayList<>(sorts.size());
 
 		for (Map.Entry<String, Sort.Direction> curSort : sorts.entrySet()) {
 			sortValues.add(new Sort.Order(curSort.getValue(), curSort.getKey()));
diff --git a/spring-batch-infrastructure/src/test/java/org/springframework/batch/item/data/MongoItemReaderTests.java b/spring-batch-infrastructure/src/test/java/org/springframework/batch/item/data/MongoItemReaderTests.java
index c01f9018d..e3d1c0d79 100644
--- a/spring-batch-infrastructure/src/test/java/org/springframework/batch/item/data/MongoItemReaderTests.java
+++ b/spring-batch-infrastructure/src/test/java/org/springframework/batch/item/data/MongoItemReaderTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2013-2020 the original author or authors.
+ * Copyright 2013-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -31,6 +31,7 @@ import org.springframework.data.domain.Sort.Order;
 import org.springframework.data.mongodb.core.MongoOperations;
 import org.springframework.data.mongodb.core.query.Query;
 
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
@@ -379,4 +380,15 @@ public class MongoItemReaderTests {
 		assertEquals(0, actualQuery.getSkip());
 		assertEquals("collection", stringContainer.getValue());
 	}
+
+	@Test
+	public void testSortThrowsExceptionWhenInvokedWithNull() {
+		// given
+		reader = new MongoItemReader<>();
+
+		// when + then
+		assertThatIllegalArgumentException()
+						.isThrownBy(() -> reader.setSort(null))
+						.withMessage("Sorts must not be null");
+	}
 }